package Segment_Tree_Basics;

/**
 * @author wly
 * @version V1.0.0
 * @date 2023/3/13 19:45
 */
public class SegmentTree<E> {
    private E[] data;
    private E[] tree;
    private Merger<E> merger;

    public SegmentTree(E[] arr, Merger<E> merger){
        this.merger = merger;
        data = (E[])new Object[arr.length];
        for (int i = 0; i < arr.length; i++) {
            data[i] = arr[i];
        }

        tree = (E[])new Object[4 * arr.length];
        buildSegmentTree(0, 0, data.length - 1);
    }

//    在treeIndex的位置创建表示区间[l...r]的线段树
    private void buildSegmentTree(int treeIndex, int l, int r){
        if (l == r){
            tree[treeIndex] = data[l];
            return;
        }

        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        int mid = l + (r - l) / 2;
        buildSegmentTree(leftTreeIndex, l, mid);
        buildSegmentTree(rightTreeIndex, mid + 1, r);

        tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
    }

    public int getSize(){
        return data.length;
    }

    public E get(int index){
        if (index < 0 || index >= data.length){
            throw new IllegalArgumentException("Index is illegal!");
        }
        return data[index];
    }

//    返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引
    private int leftChild(int index){
        return 2 * index + 1;
    }

//    返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引
    private int rightChild(int index){
        return 2 * index + 2;
    }

//    返回区间[queryL, queryR]的值
    public E query(int queryL, int queryR){
        if (queryL < 0 || queryL >= data.length ||
                queryR < 0 || queryR >= data.length || queryR < queryL){
            throw new IllegalArgumentException("Index is illegal!");
        }
        return query(0, 0, data.length - 1, queryL, queryR);
    }

//    在以treeID为根的线段树中[l...r]的范围里，搜索区间[queryL...queryR]的值
    private E query(int treeIndex, int l, int r,  int queryL, int queryR){
        if(l == queryL && r == queryR){
            return tree[treeIndex];
        }

        int mid = l + (r - l) / 2;
        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        if (queryL >= mid + 1){
            return query(rightTreeIndex, mid + 1, r, queryL, queryR);
        }else if (queryR <= mid){
            return query(leftTreeIndex, l, mid, queryL, queryR);
        }
        E leftResult = query(leftTreeIndex, l, mid, queryL, mid);
        E rightResult = query(rightTreeIndex, mid + 1, r, mid + 1, queryR);
        return merger.merge(leftResult, rightResult);
    }

    // 将index位置的值，更新为e
    public void set(int index, E e){
        if (index < 0 || index >= data.length){
            throw new IllegalArgumentException("Index is illegal!");
        }

        data[index] = e;
        set(0, 0, data.length - 1, index , e);;
    }

    // 在以treeIndex为根的线段树中更新index的值为e
    private void set(int treeIndex, int l, int r, int index, E e){
        if (l == r){
            tree[treeIndex] = e;
            return;
        }

        int mid = l + (r - l ) / 2;
        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);
        if (index >= mid + 1){
            set(rightTreeIndex, mid + 1, r, index, e);
        }else {
            set(leftTreeIndex, l, mid, index, e);
        }

        tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append('[');
        for (int i = 0; i < tree.length; i++) {
            if (tree[i] != null){
                res.append(tree[i]);
            }else {
                res.append("null");
            }
            if (i != tree.length - 1){
                res.append(", ");
            }
        }
        res.append(']');
        return res.toString();
    }
}
